This article highlights the significant challenge viral infections pose to patients with immune deficiencies, particularly after allogeneic hematopoietic cell (allo-HCT) and solid organ transplantation (SOT). It introduces virus-specific T cells (VST) therapy as a promising solution to rapidly restore antiviral immunity. The therapy involves isolating and expanding or selecting antigen-specific T cells from healthy donors and infusing them into patients. The article serves as a practical guide, covering manufacturing techniques, donor selection, and treatment indications. It summarizes nearly three decades of clinical trial data on the safety and efficacy of VSTs, discussing current challenges, limitations, and future research opportunities. This approach is significant as it offers a potential alternative to pharmacological treatments, which are often limited by efficacy, resistance, and side effects.